Catalysts such as ruthenium, osmium, rhodium or palladium are generally useful in many catalyzed chemical reactions. Often, the chemical reaction involves the synthesis or breakdown of organic chemicals, which may include polymers.
Sintering of supported metal catalysts is a common way of catalyst deactivation. To limit sintering, modifications of the support are usually made or promoters may be added to retard the rate of sintering. If both of these methods fail, the catalyzed reaction is typically run under milder conditions to slow the sintering rate. Should sintering still occur, the most typical solution is to remove the sintered catalyst from the reactor and reload with fresh catalyst. If the sintered catalyst could be regenerated, the total productive lifetime of the catalyst would be significantly increased.
Sintering (i.e., an agglomerization) during a catalyzed chemical process may occur, for example, with increased reaction temperatures, and it may vary with the type of catalyst metal, support and the reaction catalyzed because process-specific chemical complexes may form with the catalyst. Thus, characteristics of the sintered catalyst may vary.
Certain regeneration techniques for certain catalysts are known. For example:
Kearby et al., U.S. Pat. No. 3,134,732 (1964), disclose certain regeneration of certain noble metal hydrocarbon conversion catalysts after burning off carbonaceous deposits by contacting with halogen gas at a temperature of from 15.degree. C. to 677.degree. C. Platinum-containing catalysts are disclosed to be particularly suitable. A pre-reduction step is disclosed in reference to certain circumstances which relate to the platinum catalysts as saving halogenating agent.
McVicker et al., U.S. Pat. No. 3,969,267 (1976), disclose certain regeneration of reforming catalysts which comprise one or more Group VIII noble metals supported on an inert material by contacting with fluorine. Iridium-containing catalysts are disclosed to be particularly suitable.
Sennewald et al., U.S. Pat. No. 3,488,295 (1970), disclose regeneration of a certaim metallic palladium-containing catalyst by water washing; exposing to chlorine gas at an elevated temperature up to 500.degree. C.; passing air; introducing to an aqueous hydrazine hydrate solution at about 35.degree. C. to 50.degree. C.; decanting the solution; washing with water; treating with 1-30 percent aqueous alkali metal acetate solution; decanting; and drying. An O.sub.2 /N.sub.2 burning-off is optional. Specifically disclosed is a certain catalyst of metallic palladium deposited on silicic acid.
What is lacking and what is needed is a process which regenerates noble metal catalysts other than of platinum and iridium and which is highly efficient. Such process which may yield a highly active redispersed catalyst is most desirable.